1. Field of the Invention
The present invention relates to an apparatus for transmission power control in a mobile communication system, and a transmission power control method. This apparatus and method can suitably be adapted to an outer loop transmission power control in a mobile communication system which employs the CDMA (Code Division Multiple Access) system such as the W-CDMA (UTRA FDD) system.
2. Description of the Related Art
FIG. 1 illustrates a structure of a conventional mobile communication system.
Mobile communication systems conforming to various systems have been proposed and an example of the W-CDMA (UTRA FDD) mobile communication system will be described here.
In FIG. 1, numeral 1 designates a core network; 2, a radio network controller (RNC); 3, a radio base station (Node B); 4, a user equipment (UE), respectively.
The core network 1 is provided for routing in the mobile communication system. For example, the core network may be formed of the ATM switching network, a packet switching network, a router network, or the like.
The core network 1 is also connected to the other public switching networks (PSTN), enabling a user equipment (mobile station) 4 to communicate with a fixed telephone set.
The radio network controller 2 is considered as a host apparatus of the radio base station 3 and is provided with a function to control (management of radio resources used) these radio base stations 3. Accordingly the RNC can be called a base station controller also.
Moreover, the radio network controller 2 is also provided with a function to execute transmission power control (outer loop transmission power control), which will be described later, and is additionally provided with a hand-over control function to receive, under the hand-over condition, the signal transmitted from a user equipment 4 from a plurality of radio base stations 3 under the control thereof and to transmit selected data of higher quality to the side of the core network 1.
The radio base station 3 communicates with the user equipment 4 under the control of radio resources by the RNC 2.
Moreover, the radio base station 3 is also provided with a function to execute transmission power control (inner loop transmission power control), which will be described later.
The user equipment 4 establishes a radio link to the radio base station 3 when it is present within the radio area thereof and communicates with the other communication apparatus via the core network 1.
In this case, since distance between the user equipment 4 and the radio base station 3 may be changed significantly in some cases, a far-near problem, for example, is generated. However, this problem has been solved by increasing or decreasing the transmission power of the user equipment under instruction from the radio base station 3 through the outer loop transmission power control and inner loop transmission power control.
On the other hand, the transmission power of the radio base station 3 may also be increased or decreased through the outer loop transmission power control and inner loop transmission power control executed by the user equipment 4. Accordingly, multipath interference and the other cell interference may be alleviated.
An interface between the core network 1 and RNC 2 is called the Iu interface, while an interface between the RNCs 2 is called the Iur interface, an interface between the RNC 2 and each radio base station 3 is called the Iub interface, and an interface between the radio base station 3 and the user equipment 4 is called the Uu interface. The network formed by the apparatuses 2 to 3 is particularly called the radio access network (RAN).
Transmission Power Control
Next, transmission power control executed between the radio base station 3 and the user equipment 4 will be described particularly.
Transmission power control is executed for the transmitted signals of the ascending direction (up-link) and the descending direction (down-link). Here, the transmission power control of the transmitted signal in the up-link will be described.
FIG. 2 illustrates a structure of the apparatus for conducting transmission power control of the transmitted signal in the up-link.
Here, the transmission power control is assumed to be executed under the cooperation of the radio base station 3 and the RNC 2.
In FIG. 2, the elements designated by the numerals 10 to 19 are provided in the side of the radio base station 3. Numeral 10 designates an orthogonal detector, 11, a despreading part, 12, a RAKE combiner, 13, a decoder, 14, a second reception quality calculator, 15, a first reception quality measuring part, 16, a first reception quality target administrator, 17, a comparator, 18, a transmission power control signal generator, 19, a transmission processor.
The elements 20, 21 are provided in the side of the radio network controller (RNC) 2. Numeral 20 designates a second reception quality target value administrator and 21, a comparator.
Inner Loop Transmission Power Control
The inner loop transmission power control of the transmission power control will be described first.
The radio signal spread using the spreading code is received with an antenna (not illustrated) from the user equipment 4. Meanwhile, the signal obtained by implementing the frequency conversion or the like is input to the orthogonal detector 10 for separation into the in-phase component and quadrature-phase component which are input to the despreading part 11. Separate illustration of each component is omitted here.
Here, a frame format of the DPCH (Dedicated Physical Channel) of the physical channel (up-link) as the reception object will be described briefly.
FIG. 3 illustrates a frame format of the DPCH.
The DPCH includes both DPDCH and DPCCH as illustrated in the figure.
The DPDCH is a domain for storing data. For example, a transport block (transmission block) including audio data and packet data or the like is multiplexed in this domain.
The DPCCH is a domain for storing control information. The pilot signal (known signal of a predetermined pattern) as the signal used for channel estimation and SIR measurement, the TFCI (Transport Format Combination Indicator) signal indicating the multiplexing condition of the transport block, FBI signal as the signal for controlling closed loop diversity and site selection diversity and the TPC signal as the transmission power control signal for instructing increase or decrease of the transmission power of the signal transmitted to the user equipment 4 from the radio base station 3 are stored to this domain.
The DPDCH is transmitted as the in-phase component on the phase plane with the phase modulation such as QPSK (HPSK), while the DPCCH is also transmitted as the quadrature component.
The despreading part 11 executes the despreading process to the received signal and applies the despread signal to the RAKE combiner 12 and the first reception quality measuring part 15.
The user equipment 4 respectively implements the spreading process using the channelization code for channel separation to the DPDCH and DPCCH and also implements the spreading process using the scrambling code for identification from the other user equipment to both DPDCH and DPCCH. Therefore, the despreading part 11 implements the despreading process using both scrambling code and channelization code.
The first reception quality measuring part 15 measures the first reception quality (for example, SIR (Signal to Interference Ratio)) using the pilot signal included in the DPCCH as the quadrature component of the DPCH and then inputs the result of the measurement to the comparator 17. It is also possible here to conduct the SIR measurement on the basis of the pilot signal after the RAKE combining in the RAKE combiner 12.
The comparator 17 compares the target reception quality (target SIR) given from the first reception quality target administrator 16 with the result of measurement (measured SIR) from the first reception quality measuring part 15 and applies the comparison result to the transmission power control signal generator 18.
The transmission power control signal generator 18 generates, when the measured SIR is smaller than the target SIR based on the comparison result, the TPC signal for instructing an increase in the transmission power and applies this TPC signal to the transmission processor 19.
Meanwhile, when the measured SIR is larger than the target SIR, the transmission power control signal generator 18 generates the TPC signal for instructing decrease of the transmission power and then applies this TPC signal to the transmission processor 19.
The transmission processor 19 transmits the TPC signal to the user equipment 4 together with the other data which must be transmitted to the user equipment 4 via the down-link.
Accordingly, the user equipment 4 increases or decreases the transmission power to the radio base station 3 on the basis of the TPC signal received from the radio base station 3.
As will be apparent from the control method, the received signal from the user equipment 4 is subjected to the transmission power control to make the SIR closer to the target SIR without regardless of the location of the user equipment 4. Accordingly, the far-and-near problem can be solved.
The basic operations of the inner loop transmission power control is described above and the outer loop transmission power control is then described below.
Outer Loop Transmission Power Control
The received signal despread by the despreading part 11 is then input to the decoder 13.
As illustrated in the figure, the decoder 13 is given the data (transport block) stored in the DPDCH and the TFCI signal stored in the DPCCH.
Here, the TFCI is the information indicating the multiplex condition of the transport block stored in the multiplex mode in the DPDCH and a plurality of multiplexed transport blocks can be demultiplexed.
Accordingly, the decoder 13 extracts each transport block on the basis of the TFCI, performs the decoding process to respective blocks (for example, the audio signal can be viterbi-decoded and the packet data can be turbo-decoded), and outputs the result of decoding.
The decoded data is then transmitted to the side of the radio network controller 2 and is also input to the second reception quality calculator 14.
The second reception quality calculator calculates, for example, error quality (CRC error or no CRC error, bit error rate, block error rate, or the like) and transmits the same to the comparator 21 in the side of the radio network controller 2.
Here, a typical method for calculating error quality will be described.
CRCI (Cyclic Redundancy Check Indicator)
CRC check result of the received one transport channel (here, designated as RAB#1 or the like which is one of the channels for transmitting audio data) is measured and the result of the measurement is calculated as error quality.
In particular, the CRC check is conducted using the CRC check bit included in the decoded data obtained by decoding the signal received within the radio frame corresponding to the TTI (Transport Time Interval) period unit (for example, 20 ms) via the transport channel (RAB#1) including the audio data and the check result (including error or non-error) is calculated as the error quality.
The typical error quality calculating method has been described above and the error quality obtained with any of the calculating methods is given to the comparator 21 of the radio network controller 2 via the Iub interface.
The comparator 21 obtains a target value of the second reception quality, which is the quality value required for the transport channel (for example, RAB#1, one of the channels for transmitting the audio data) from a second reception quality target value administrator 20, and compares the same with the reception quality from the second reception quality calculator 14 to perform update control of the target value of the first reception quality administrated (stored) by the first reception quality target value administrator 16.
Namely, when the reception quality calculated by the second reception quality calculator 14 is found to be lower than the target value of the second reception quality as a result of comparison, update control is performed to raise (by addition of +d) the target value (target SIR) of the first reception quality.
Meanwhile, when the reception quality calculated by the second reception quality calculator is found to be higher than the target value of the second reception quality as a result of comparison, the update control is performed to lower (by addition of −d) the target value (target SIR) of the first reception quality.
With the outer loop control as described above, the target SIR is updated on the basis of the reception error quality, it is possible to prevent occurrence of the event that control for increasing transmission power is not performed even when the reception error is lower than the predetermined error quality.
Multi-Call
Finally, encoding process under the multi-call state will be described.
Here, an example where the second reception quality calculator 14 designates the transport channel as the object of calculation of reception quality to the transport channel for transmitting audio data will be described.
FIG. 4 is a diagram for describing multiple processes (for up-link) of the transport channel.
In this figure, 321 to 324 designate encoding processors of each transport channel. 29 designates a transport channel multiplexer; 30, a second interleave part; 31, a physical channel mapping part, respectively.
Here, 321 to 323 designate transport channels for audio data; 324, a transport channel for packet data.
To each transport channel encoding processor 321 to 324, transport block (transmission data block) is input in every TTI from an upper layer.
FIG. 5 is a diagram indicating transport block sizes when the AMR (adaptive multi-rate) encoding (12.2 kbps) is performed on the audio signal input to the user equipment 4.
When the AMR encoding is adopted, the encoded data is output as the data classified into class A (RAB#1), B (RAB#2), and C (RAB#3) in accordance with the importance thereof.
For example, in the signaling state (voice existing state), the data of 81 bits is output as class A in every TTI (for example, 20 ms), the data of 103 bits is output as class B and the data of 60 bits is output as class C.
When the background noise is output, the data of 39 bits is output as class A in every TTI (for example, 20 ms). In this case, the data of class B and class C are not output. In the non-signaling state (voice non-existing state), no data of class A, B, and C is output in every TTI (for example, 20 ms).
Here, the encoding processors 321 to 323 of each transport channel to which the data of classes A, B, and C are input in every TTI perform the encoding process for the input data. The packet data is input in every TTI to the encoding processor 324 of the transport channel, but such packet data is never input when there is no packet data to be transmitted.
For the class A and packet data, the CRC check bit of 12 bits, as the result of CRC calculation conducted by a CRC adder 22, is added. In the case of classes B and C, no CRC check bit is added. Moreover, in the case of class A, the predetermined bits are output as the CRC bits even under the non-signaling state (when 0 bit is input).
The packet data is output, with addition of the CRC check bit, respectively to the transport blocks input in every TTI.
Next, a code block segmentation part 23 divides a code block into a plurality of blocks as required (for example, when the code block is too long, or the like) before the channel encoding process. Each block is then encoded with a channel encoder 24.
The classes A and B are convolution-encoded at an encoding rate of ⅓, while the class C, at an encoding rate of ½, in accordance with a degree of importance. Meanwhile, the packet data is turbo-encoded in the encoding rate of ⅓. In regard to the packet data, each datum to which the CRC check bit is added is preferably turbo-encoded at a time.
The data after the channel encoding is then input to a radio frame equalizer 25 for bit adjustment through addition of bits or the like so that the data can be divided, resulting in no remainder with a value obtained by n=TTI/10 ms.
The data after bit adjustment is interleaved (re-arrangement process) with a first interleave part 26, and is then divided into data portions with a radio frame divider 27. Thereafter, each data portion after the division is then sequentially (for example, in every 10 ms) input to a rate matching part 28.
The rate matching part 28 tries to apply data into the radio frame through repetition and puncture (curtailment) to give redundancy to each data (processed respectively by the encoding processors 321 to 324) in accordance with a degree of importance so that the total sum of the data sequentially output from the encoding processors 321 to 323 of each transport channel is accommodated within one radio frame.
Accordingly, the transport channel multiplexer 29 multiplexes, on the time axis, the transport blocks output, every 10 ms, from the encoding processors 321 to 323 of each transport channel and gives the data to the second interleave part 30 as the data accommodated within one radio frame.
The second interleave part 30 interleaves the data after the multiplex process executes the mapping to the physical channel with the physical channel mapping part 31 to realize signal transmission of the up-link via the physical channel.
By the way, if the state of the multiplexed transport block is not indicated to the radio base station 3, it is very difficult for the radio base station 3 to demultiplex the multiplexed transport blocks.
Therefore, the number of transport blocks (TBs) transmitted in the TTI period and the size of a transport block (TB) are indicated with a value of the transport format indicator (TFI) and moreover a value of the transport format combination indicator (TFCI) is assigned to a combination of the TFI of a radio access bearer.
Here, since the TFCI is the information indicating the state of multiplex process, it may be called the multiplex state information.
Assignment of the transport format indicator (TFI) during the multi-call transmission of the audio transmission (up-link: 12.2 kbps) and the packet transmission (down-link: 32 kbps) and the transport format combination (TFCI) is shown in FIGS. 6A, 6B.
In this case, the transport format combination indicator (TFCI) includes nine indicators C0 to C8, and these indicators are transmitted to the radio base station 3 (Node-B) from the user equipment (UE) 4 via the DPCCH. In the radio base station 3, the decoding process and demultiplex process into the transport block (TB) of each radio access bearer (RAB) are conducted by detecting the transport format with the received transport format combination indicator (TFCI).
As the prior art documents of the present invention, the patent document 1 (Pamphlet of International Laid-Open Patent: No. 47253/1998) describes the CDMA communication method to realize improvement in application efficiency of frequency resources and in communication quality by transmitting the control information (pilot symbol and TPC symbol) through an increase in transmission power only with the designated one individual physical channel in the multi-code transmission. Moreover, the patent document 2 (Japanese Unexamined Patent Publication No. 2001-217770) describes transmission power control to eliminate the occurrence of mismatching in the outer loop control before and after execution of the hand-over connection. Moreover, the patent document 3 (Japanese Unexamined Patent Publication No. 2001-285193) describes the outer loop transmission control to maintain the predetermined communication quality respectively in a plurality of channels even when only one bit may be used as the transmission control bit to the user equipment from the base station. Moreover, the patent document 4 (Japanese Unexamined Patent Publication No. 2003-18089) describes the radio communication apparatus, which can maintain the reception quality to the desired quality regardless of change in the propagation environment in the outer loop transmission power control.
When the calculation object of the second reception quality for the outer loop transmission power control during the multi-call process is designated to the channel (transport channel) for data transmission (for example, CRC bit described previously) even in the non-signaling state, it is preferable because the outer loop transmission power control can be executed continuously more than that when the object is designated to the channel for the packet data transmission.
However, a problem is usually generated when the outer loop transmission power control is executed on the basis of the data which allows change of the encoding rate.
For example, when the CRC bit is added, in C bits, to the audio data X(bit) and the data is encoded by the convolution-encoding process (encoding rate: ⅓), the number of bits Y after the encoding is expressed by the following formula.Y=(X+C+T)×3
Where, T is the number of tail bits coupled to the last part of the code block before the encoding process. T is 8 bits. C is the number of CRC check bits and it is 12 bits.
Here, the encoding rate in the signaling state is obtained accurately. Since X is 81,
                    R1        =                              (                          X              +              C                        )                    /                      {                                          (                                  X                  +                  C                  +                  T                                )                            ×              3                        }                                                  =                                            (                              81                +                12                            )                        /                          (                              81                +                12                +                8                            )                                ×          3                                        =                  1          /          3.26                    
Moreover, the encoding rate in the background noise state is obtained accurately. Since X=39,
                    R2        =                              (                          X              +              C                        )                    /                      {                                          (                                  X                  +                  C                  +                  T                                )                            ×              3                        }                                                  =                                            (                              39                +                12                            )                        /                          (                              39                +                12                +                8                            )                                ×          3                                        =                  1          /          3.47                    
Moreover, the encoding rate in the non-signaling state is obtained accurately. Since X=0,
                    R3        =                              (                          X              +              C                        )                    /                      {                                          (                                  X                  +                  C                  +                  T                                )                            ×              3                        }                                                  =                  12          /                      {                                          (                                  12                  +                  8                                )                            ×              3                        }                                                  =                  1          /          5                    
Even when the convolution-encoding rate is set identically to ⅓, the encoding rate in the non-signaling state becomes small because the rate of the tail bits becomes high in the number of bits input to the encoder. Accordingly, the encoding rate becomes smaller in the sequence of the signaling state, background noise state, and non-signaling state.
Since bit error is corrected to a larger extent in the decoding process when the encoding rate is smaller, error quality calculated by the second reception quality calculator 14 for the data in the non-signaling state becomes higher than that in the background noise state and the error quality calculated by the second reception quality calculator 14 for the data in the background noise state becomes higher than that in the signaling state.
Therefore, as illustrated in FIG. 7, the packet and DCCH are likely to be controlled to satisfy the desired quality in the signaling state because the target SIR is update-controlled with the outer loop control to satisfy the predetermined quality of the AMR on the basis of the error quality of AMR calculated by the second reception quality calculator 14 but the packet and DCCH does not satisfy the respective desired quality in the non-signaling state because the error quality of AMR calculated by the second reception quality calculator 14 shows comparatively higher quality and thereby the target SIR is lowered by the outer loop control.
Moreover, when the data obtained by conducting the error correction encoding (channel encoding) and then executing the interleave process to the transmitting block is transmitted through division into a plurality of radio frames, if the number of radio frames N at the dividing destination changes, the durability for burst error when a value of N becomes larger is intensified. Therefore, excellent error quality can be calculated with the second reception quality calculator 14, resulting in a similar problem.
When the data as the object of monitoring by the second reception quality calculator is not audio data but other data such as packet data, durability for burst errors may also be considered to change due to changes in encoding rate and the number of radio frames N at the dividing destination.
Moreover, even in the single-call state in place of the multi-call state, if the target value of the first reception quality is lowered because the non-signaling state is continued in the audio data, a problem is also generated, in which reception fails in the signaling state.